1. Field of the Invention
The invention relates to a connecting structure for male and female terminal fittings.
2. Description of the Related Art
U.S. Pat. No. 7,150,660 and FIG. 10 herein disclose a connecting structure for high-current terminal fittings. As shown in FIG. 10, this connecting structure has a male terminal 1 with a tab 2 in the form of a relatively thick tongue and a female terminal 3 with a rectangular connecting tube 4 into which the tab 2 is to be inserted. A louver spring 5 is housed in the connecting tube 4. The louver spring 5 has two contact piece rows each including a plurality of juxtaposed resilient contact pieces 6. The contact piece 6 has contact portions 6A arranged to face each other while being spaced apart. On the other hand, inclined surfaces 7 are formed on opposite surfaces of a tip of the tab 2 and taper the tip for guiding purposes.
The tab 2 of the male terminal 1 is guided into the louver spring 5 when being inserted into the connecting tube 4 of the female terminal 3 and thrusts itself between the contact portions 6A at the opposite sides while resiliently displacing the rows of the resilient contact pieces 6 at the opposite sides. Thus, the tab 2 is sandwiched resiliently between the contact portions 6A at the opposite sides for electrically connecting the tab 2 and the louver spring 5, and consequently the male and female terminal fittings 1, 2.
A variation of an insertion force of the tab 2 is shown by a characteristic curve x of FIG. 9. Specifically, the tip of the tab 2 contacts the contact portions 6A of the resilient contact pieces 6 at the opposite sides and then the tab 2 is pushed in while resiliently displacing the resilient contact pieces 6, i.e. receiving an insertion load to gradually increases. The tab 2 receives a largest load when base end edges 7A of the inclined surfaces 7 pass the contact portions 6A and then the load gradually decreases. More particularly, a load peak is reached when the tab 2 is inserted a predetermined distance after the base end edges 7A of both inclined surfaces 7 contact the contact portions 6A. This is thought to be because the base end edges 7A pass the contact portions 6A at a delayed timing due to a backward displacement of the louver spring 5 or inclination of the resilient contact pieces 6 resulting from a housing tolerance of the louver spring 5. At any rate, this conventional connecting structure is such that the base end edges 7A of both inclined surfaces 7 on the tip of the tab 2 simultaneously pass the contact portions 6A of the rows of the resilient contact pieces 6 at the opposite sides. Thus, a large insertion load is received during a connecting operation, i.e. a large insertion force (about 75N) is necessary, which has been a problem in ensuring a smooth connecting operation.
The present invention was developed in view of the above situation and an object thereof is to reduce an insertion force by a simple structural change.